The development of hybridoma technology made it possible to generate cell lines producing monoclonal antibodies (MAbs) of desired specificity which can be used to identify, isolate and characterize biologically important molecules.
The MAbs which are subject of the present invention are directed against carcinoembryonic antigen (CEA). CEA is a complex immunoreactive glycoprotein with a molecular weight of 180,000 found in adenocarcinomas of endodermally derived digestive system epithelia and foetal colon. The role of CEA immunoassays for diagnosis and serially monitoring cancer patients for recurrent disease or response to therapy (Mach et al., Immun. Today 2, 239, 1981; Berche et al., Br. Med. J. 285, 1447, 1982) as well as their use in experimental models of nude mice bearing human colon carcinoma xenografts (Hedin et al., Int. J. Cancer 30, 547, 1982; Buchegger et al., Int. J. Cancer 33, 643, 1984) have been widely evaluated and documented.
One of the major drawbacks of the use of anti-CEA antibodies for clinical purposes has been the cross-reactivity of these antibodies with some apparently normal adult tissues. Previous studies have shown that most conventional hyperimmune antisera raised against different immunogenic forms of CEA cross-react with many different types of carcinomas as well as CEA-related antigens found in normal colonic mucosa, spleen, liver, lung, sweatglands, polymorphonuclear leukocytes and monocytes of apparently normal individuals. The first of the series of identified antigens cross-reacting with CEA was called normal glycoprotein (NGP) or non-specific cross-reacting antigen (NCA) by Mach and Pusztaszeri (Immunochemistry 9, 1031, 1972) and by von Kleist et al. (Proc. Natl. Acad. Sci. 69, 2492, 1972), respectively. Here, it will be referred to as NCA.sub.55, because it was shown by both research groups to have a molecular weight of about 55 kD. This antigen has also been described by several other research groups under different names, including CCEA-2 (Tuberville et al., Immunochemistry 10, 841, 1973), CCA-III (Primus et al., J. Immunol. 118, 55, 1977) and TEX (Kessler et al., Cancer Res. 38, 1041, 1978). Buchegger et al. (Int. J. Cancer 33, 643, 1984) identified a CEA cross-reacting antigen of 95 kD (NCA.sub.95). Another antigen very closely related to CEA in terms of cross-reactivity and molecular weight (160 kD) was described by Burtin et al. (in: Fishman & Sell, Onco-developmental gene expression, N.Y. 1976, pp. 609-611) and was designated NCA-II. This antigen appears to be very similar to the normal fecal antigen-2 (NFA-2) described by Matsuoka et al. (Int. J. Cancer 21, 604, 1978). The same group identified in normal adult feces a CEA-related glycoprotein of 20-30 kD called NFA-1 (Kuroki et al., Mol. Immunol. 19, 399, 1982). Finally, biliary glycoprotein-1 (BGP-1) is an antigen cross-reacting with CEA present in normal bile described by Svenberg (Int. J. Cancer 17, 588, 1976). These results as a whole demonstrate that antisera recognize epitopes specific for CEA alone as well as epitopes present on both CEA and CEA-related antigens; they further suggest closely related genes between CEA and CEA-related antigens as well as precursor-product relationships between some of them. According to Hammarstrom et al. (Proc. Natl. Acad. Sci. 72, 1528, 1975) and Hedin et al. (Mol. Immunol. 23, 1053, 1986) the epitopes are predominantly located on the peptide moieties of CEA and appear to be strongly conformation dependent.
The production of monoclonal anti-CEA antibodies is disclosed by several research groups. Accolla et al. (Proc. Natl. Acad. Sci. 77, 563, 1980) reported that antibodies obtained from two hybridoma clones reacted strongly with CEA but also weakly with NGP. The reactions of these two antibodies with CEA were not competitively inhibited by each other indicating that they react with different antigenic determinants on the CEA molecule. The antibodies described by Kupchik et al. (Cancer Res. 41, 3306, 1981) and Primus et al. (Cancer Res. 43, 686, 1983) have been shown to have at least some degree of reactivity with normal polymorphonuclear leukocytes (PMNs). Kuroki et al. (J. Immunol. 30, 2090, 1984) described two MAbs against CEA which, however, do not react with purified CEA preparations other than those used for immunization. These MAbs have not yet been characterized as to the range of reactivity to tumour versus normal tissues.